(1) Field of the Invention
The present invention relates to a circuit for driving a liquid crystal display (LCD) having a power saving feature. More specifically, the present invention relates to a circuit for driving an LCD having a power saving feature, in which an invalid data interval showing no data output is sensed, so that no power would be supplied to an LCD panel during the invalid data interval, thereby making it possible to significantly reduce power consumption.
(2) Description of the Prior Art
In accordance with the trend of compactness and lightness in weight of electronic apparatuses, studies and researches are being briskly carried out to obtain a plane (i.e., twin panel) display for replacing the cathode ray tube (CRT).
Of the plane displays, the LCD requires a low voltage and a low driving power, to such a degree that an LSI driver can be used in driving it. Further, an LCD is thin and light in weight, and therefore, many makers have concentrated efforts to put the LCDS to a practical use.
Referring to the attached drawings, a conventional LCD driving circuit will be described.
FIG. 1 is a block diagram showing a conventional LCD driving circuit.
As shown in FIG. 1, the conventional LCD driving circuit includes: a timing section 10 with its input terminals connected to a vertical synchronizing signal line VSYNC, to a horizontal synchronizing signal line HSYNC, and to a data signal line DATA; an LCD power source section 20 with its input terminals connected to a power source voltage VDD, and to an output terminal of the timing section 10; a data driving section 30 with its input terminals connected to the timing section 10 and to an output terminal of the LCD power source section 20; a scanning driving section 40 with its input terminals connected to the timing section 10 and to an output terminal of the LCD power source section 20; and an LCD panel 50 with its input terminals connected to the data driving section 30 and to the scanning driving section 40.
The above described conventional LCD driving circuit operates in the following manner.
The timing section 10, which consists mainly of a gate array, receives external video signals such as vertical synchronizing signals VSYNC, horizontal synchronizing signals and data signals, so as to supply the data signals to the data driving section 30, and so as to supply starting signals STV to the scanning section 40 in a controlled manner at proper timing.
FIG. 2 is a timing chart for the conventional LCD driving circuit.
As shown in FIG. 2, the timing section 10 begins to output data signals DATA together with the starting signals STV after passing of a horizontal synchronizing signal HSYNC from the time of beginning of a vertical synchronizing signal VSYNC. The timing section 10 completes the outputting of the data signals DATA before the generation of a horizontal synchronizing signal HSYNC from the end of a vertical synchronizing signal VSYNC.
The horizontal synchronizing signals HSYNC of 525 H periods correspond to an interval of the vertical synchronizing signals VSYNC of 1V periods. Of the 525 H periods of the horizontal synchronizing signals HSYNC, the valid data intervals of the data signals DATA are 480 H periods. Therefore, 525 H periods of the horizontal synchronizing signals HSYNC less 480 H periods of the valid data intervals equals to 45 H periods, and these 45 H periods correspond to invalid data intervals.
If data signals DATA are supplied from the timing section 10 during the valid data intervals, the data driving section 30 outputs to the LCD panel 50 a gradation voltage corresponding to the data signals, so that the line data selected by the scanning driving section 40 is displayed.
The scanning driving section 40 selects the lines of the LCD panel 50 for each period of the horizontal synchronizing signals HSYNC, so that the data is displayed. This is repeatedly carried out, thereby displaying pictures on the screen.
However, in the above described conventional LCD driving circuit, power is supplied even during the invalid data interval, with the result that a corresponding portion of the power is squandered. That disadvantage is a sensitive problem in a battery-driven portable computer.